1. Field of the Invention
This invention relates to a pretreatment process for a deposition chamber. More particularly, this invention relates to a pretreatment process for treating the surfaces of a deposition chamber, after a cleaning step and prior to deposition of a materials such as tungsten silicide on a substrate.
2. Description of the Related Art
In the deposition of a material such as a tungsten silicide on a substrate, residues from the deposition process, e.g., tungsten silicide residues, may also be deposited on the surfaces of the deposition chamber, including the chamber walls and the susceptor used to support the substrate in the deposition chamber. Repeated tungsten silicide depositions results in the buildup of such undesirable residues on the deposition chamber surfaces. To prevent such residues from flaking off the chamber surfaces, which would result in contamination of the substrate being processed in the chamber, the chamber is subject to periodic cleaning to remove such deposition residues. The removal of such tungsten silicide residues from the deposition chamber surface may be accomplished by the use of a fluorine-containing etchant such as NF.sub.3 or C.sub.2 F.sub.6 gas.
Normally, the cleaning of the chamber is performed using a plasma in conjunction with such fluorine-containing etchant gases and may be followed by a passivation treatment with hydrogen to remove fluorine-bearing residues remaining in the chamber. However, in the subsequent deposition of tungsten silicide, after such a cleaning treatment, it has been found that the initial substrate subsequently mounted on the susceptor is not adequately receptive to the deposition of a layer of tungsten silicide.
Thus, the tungsten silicide, deposited on the initial or first substrate processed after cleaning, is of inferior quality and must be rejected. This, of course, is not only a rejection or loss of the cost of the tungsten silicide layer but also is a rejection or loss of any other structure previously formed on the substrate, e.g., an integrated circuit structure created to that point on a semiconductor wafer. It will be seen that the loss is not insubstantial. If the vacuum chamber is cleaned, for example, after every tenth wafer treated with tungsten silicide, the number of wafers rejected can amount to ten percent.
This problem is most apparent when a combination of a tungsten-bearing gas such as WF.sub.6 is used in connection with a chlorine-substituted silane gas such as dichlorosilane (DCS). Since the formation of a tungsten silicide layer using a chlorine-substituted silane gas has been found to provide step coverage over an uneven substrate surface superior to the use of silane itself, it is important that a way be found to periodically clean the deposition chamber to remove undesired deposition residues without, however, interfering with subsequent depositions of tungsten silicide on substrates, and in particular, without incurring the inferior deposition of tungsten silicide on the first or initial substrate processed after such a cleaning of the vacuum chamber.
In a prior application, Telford et al. Ser. No. 07/968,710, filed Oct. 30, 1992, and assigned to the assignee of this case, it was proposed to use an aluminum nitride-coated graphite susceptor for a substrate, when forming tungsten silicide thereon, because of the higher deposition temperatures normally associated with the formation of tungsten silicide materials. While the graphite susceptor was more resistant to warpage, etc, than conventional aluminum susceptors, the use of an aluminum nitride coating over the graphite surfaces was found to be necessary to provide sufficient corrosion resistance to the graphite susceptor.
While such an aluminum nitride-coated graphite susceptor was found to be useful in the formation of tungsten silicide at elevated temperatures, e.g., temperatures in excess of about 400.degree. C., the above problems concerning the deposition of tungsten silicide on a first substrate after a cleaning step were first discovered during the use of such a coated susceptor in connection with the formation of tungsten silicide on a substrate on the susceptor using a tungsten fluoride/dichlorosilane gas combination. Therefore, in our parent application Telford et al. Ser. No. 08/083,420, the disclosure of which is hereby incorporated by reference, we addressed this problem by proposing a pretreatment or conditioning to be carried out on the susceptor in the deposition chamber after each cleaning operation, and prior to the processing of the first substrate after such a cleaning step.
In particular, we taught a preconditioning treatment in which, after the cleaning of the deposition chamber, a deposition of tungsten silicide was carried out in the chamber, without a substrate on the susceptor, and using a combination of a tungsten-bearing gas such as WF.sub.6 ; a chlorine-substituted silane gaseous silicon source such as, for example, dichlorosilane (SiH.sub.2 Cl.sub.2), monochlorosilane (SiH.sub.3 Cl), or trichlorosilane (SiHCl.sub.3); and a carrier gas, such as argon or helium.
While this precoating or preconditioning procedure, as described and claimed in our parent application, resulted in the subsequent formation of a satisfactory coating of tungsten silicide on even the first substrate processed in the chamber after a cleaning step, it was found that in some instances, particularly when a chlorosilane was used in the preconditioning treatment, subsequent deposits on substrates, e.g., after the processing of 10 or more substrates, resulted in the eventual build up of residues on the chamber surfaces, including the susceptor surfaces which tended to more readily flake off and form particles than previously deposited residues on the chamber surfaces.
While we do not wish to be bound by any theories, it appears that when a chlorosilane-based tungsten silicide deposit was made, to precondition the susceptor and any other aluminum-bearing chamber surfaces deposited upon in situ, the resultant deposit did not form a good bond to the underlying aluminum-bearing surfaces, apparently due to the stressed nature of the chlorosilane-based tungsten silicide material deposited thereon.
Thus, the solution to the problem of an inferior formation of tungsten silicide on the first substrate processed after a cleaning step, in turn, seemingly created a separate problem which needs to be solved.